This invention relates to the production of olefin polymers by polymerization with a magnesium alkoxide polymerization catalyst. More particularly, the present invention relates to the improvement of the productivity of polymerization catalysts formed from magnesium alkoxides which normally undergo poor metathesis towards production of magnesium chloride.
Experience has shown that the best magnesium chloride supported titanium tetrahalide catalysts for olefin polymerization are prepared via metathesis of a suitable magnesium compound rather than forceful mechanical and chemical treatment of magnesium chloride. Very good commercial polymerization catalysts have been prepared via metathesis of magnesium ethoxide using titanium tetrachloride in the presence of an ester and, optionally, a halohydrocarbon as disclosed in U.S. Pat. Nos. 4,400,302 and 4,414,132. It is difficult to cause the reaction between magnesium metal and ethanol and therefore magnesium is usually activated in some fashion before attempting the reaction with ethanol. Furthermore, it is extremely difficult to precipitate product (and therefrom to prepare catalysts) of controllably uniform particle size and shape. On the other hand, magnesium reacts quite exothermally with methanol to give relatively stable solutions of magnesium methoxide in methanol at room temperature. Despite the synthetic convenience of magnesium methoxide, the commercially available solid material has proven intractable towards direct metathesis with traditional chlorinating agents such as silicon- or titanium tetrahalides. It is purported that magnesium methoxide does not metathesize well because of the extreme thermodynamic stability of the polymeric forms, [Mg(OMe).sub.2.MeOH].sub.n and [Mg(OMe).sub.2 ].sub.n which are formed either upon evaporation of methanol from a Mg (OMe).sub.2 solution or as an insoluble precipitate upon boiling a methanolic Mg(OMe).sub.2 solution.
It is an object of the present invention to utilize the ease of reaction of magnesium with methanol and capitalize upon the high solubility of the reaction product in order to produce a superior catalyst precursor. A further object is to cause a beneficial transformation into magnesium ethoxide then to utilize the ease of metathesis of magnesium ethoxide to produce a highly effective polymerization catalyst.